Experimental Cross Sections for Charge-Changing Collisions ofHe+andHe++Ions Traversing Gases

Ion beams of ${\mathrm{He}}^{+}$ and ${\mathrm{He}}^{++}$, in the kinetic energy range 100 to 450 kev, are held in arcs of circular orbits in a magnetic field. When a few microns of gas are admitted the beam is attenuated by charge-changing collisions, since with change of charge the ion is lost from its orbit. Cross sections for such charge-changing collisions are designated by ${\sigma }_{\mathrm{if}}$, where $i$ is the initial positive ionic charge in electron units and $f$ the charge after the collision. (${\sigma }_{10}+{\sigma }_{12}$) has been directly measured for ${\mathrm{He}}^{+}$ in hydrogen, helium, and air, and (${\sigma }_{21}+{\sigma }_{20}$) for ${\mathrm{He}}^{++}$ in the same gases.